A related copending United States patent applications commonly owned by the assignee of the present document and incorporated by reference in their entirety into this document is being filed in the United States Patent and Trademark Office on or about the filing date of this application. This application is Hewlett-Packard Company docket number 10004232-1 and is titled xe2x80x9cLOW COST DETECTION OF WOBBLE INVERSIONS USING A BANDPASS TUNED CIRCUIT.xe2x80x9d
This invention relates generally to storing data on optical disks. In particular, it relates to detecting digital data written on a clock reference structure formed on a servo track.
Some optical disk standards have a permanent clock reference structure formed continuously along servo tracks. This clock reference structure provides a clock reference signal that is generated by an optical transducer as the clock reference structure passes by the optical transducer as the optical disk rotates. One such optical disk standard is called DVD+RW. DVD+RW is specified by the European Computer Manufacturers Association (ECMA) in several standards and draft standards. Many of these standards and draft standards are available at http://www.ecma.ch or by ordering them from ECMA, 114 Rue du Rhxc3x4ne, CH-1024 Geneva, Switzerland. One such draft standard is titles xe2x80x9c120 mm ReWriteable DVD (DVD+RW) Capcity: 4,7 Gbytes and 9,4 Gbytesxe2x80x9d dated Feb. 1999 which is hereby incorporated herein by reference.
This draft standard specifies that the rewriteable area contain a phase modulated deviation from the nominal centreline called wobble. This wobble provides a permanent clock reference structure and also contains addressing information called Address-in-Pregroove or ADIP. The ADIP data is placed on the track using bi-phase shift keying (BPSK). In other words, a xe2x80x9c0xe2x80x9d is represented on the disk by a wobble with a first phase angle and a xe2x80x9c1xe2x80x9d is represented on the disk by a wobble that is 180xc2x0 different from that first phase angle. The transitions between these two phases are called wobble inversions.
Accordingly, there is a need in the art for a means of detecting wobble inversions. This means should have good noise immunity and not be sensitive to low frequency shifts of the wobble signal. This means should also be inexpensive to produce and require as little circuitry as possible.
In a preferred embodiment, the invention utilizes a tuned circuit that filters out noise and also generates a transient at the point the wobble inversion occurs. This transient can be cleanly detected to determine the presence of a wobble inversion. The invention is easily tuned to accommodate different wobble frequencies and is well adapted to inexpensive fabrication. The present invention may be implemented as tuned circuit with a natural frequency slightly below the wobble frequency. When a wobble inversion occurs, the tuned circuit reacts by outputting a transient with an amplitude greater than that of the output signal when a wobble inversion does not occur. This transient can be detected by a simple threshold detector.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.